<template>
    <ul class="list">
        <li class="item" v-for="item of  letters" :key="item" :ref="item"  @touchstart.prevent="handleTouchStart"  @touchmove="handleTouchMove"  @touchEnd="handleTouchEnd"   @click="handleLetterClick">
            {{item}}
        </li>
    </ul>
</template>
<script>
export default {
  name: "cityAlphabet",
  props: {
    cities: Object
  },
  computed: {
    letters() {
      const letters = [];
      for (let i in this.cities) {
        letters.push(i);
      }
      return letters;
    }
  },
  data() {
    return {
      touchStatus: false,
      touchY: 0,
      timer: null
    }
  },
  updated () {
      this.startY = this.$refs["A"][0].offsetTop
  },
  methods: {
    handleLetterClick(e) {
      this.$emit("change", e.target.innerText);
    },
    handleTouchStart() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        const touchY= e.touches[0].clientY - 79
        const index= Math.floor((touchY - this.startY) / 20)
        if (index >=0 && index < this.letters.length) {
             this.$emit("change",this.letters[index])
        }
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl';

.list {
    position: absolute;
    display: flex;
    flex-direction: column;
    justify-content: center;
    top: 1.58rem;
    right: 0;
    bottom: 0;
    width: 0.4rem;
}

.item {
    text-align: center;
    line-height: 0.4rem;
    color: $bgColor;
}
</style>
